In recent years, in the field of gas cutting, for example, a cutting method using hydrogen in place of acetylene gas or propane gas has received attention. When cutting is performed using hydrogen, a small amount of a hydrocarbon gas is added so that a flame is visible.
In this manner, a mixing device using a pressure regulator for equalizing pressures of gases and a flow rate regulating valve for setting each gas at a predetermined ratio by regulating a flow rate when a mixed gas is generated by mixing two types of gases is conventionally known.
In such a conventional gas mixing device, the pressure of each gas is set and regulated by the pressure regulator provided in correspondence with each gas. In general, when a flow rate (used amount) fluctuates, the pressure of the gas passing through each pressure regulator fluctuates. When the used amount of the mixed gas discharged from the gas mixing device increases/decreases and therefore a passing flow rate of each gas increases/decreases, the pressure of each gas set in each pressure regulator may fluctuate with respect to set pressure and a ratio of the gases constituting the mixed gas may deviate from a set value.
In this manner, when the used amount of the mixed gas has increased/decreased, it is necessary to set a mixture ratio to a predetermined ratio by resetting pressures of gases to the same pressure and regulating the flow rate of each gas passing through each flow rate regulating valve again.
Therefore, technology for equalizing pressures of the gases by regulating differential pressure using a differential pressure regulating valve, a pressure balance circuit, or the like or by setting regulated pressure of one gas as pilot pressure using a pilot pressure regulator and controlling a pressure regulator of the other gas to set pressure of the other gas to the same pressure as that of the one gas is disclosed (for example, see Patent Literature 1).